1. Field of the Invention
The present invention relates to a mark position detection apparatus for detecting the position of a overlay mark or an alignment mark provided on a substrate to be detected such as a semiconductor wafer or the like.
2. Related Background Art
In the conventional semiconductor manufacturing process, it is necessary to measure the amount of positional displacement between a resist pattern formed by a photolithography process and an underlying pattern. Overlay measuring apparatuses for measuring an amount of displacement in superposition have been proposed (for example in Japanese Patent Application Laid-Open No. 2000-77295).
The apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-77295 measures the amount of displacement in overlay by illuminating a measurement mark with illumination light, focusing light reflected from the measurement mark by an imaging optical system to form an image, picking up the image by an image pickup apparatus such as a CCD camera, and processing the image. In this apparatus, the wavelength range of the illumination light is so wide as to include visible light and near-infrared light in order to obtain stable reflection light intensity for various types of measurement mark structures.
In the case that an overlay error is measured optically, optical aberrations in the measurement optical system (that is, an illumination optical system for illuminating a measurement mark with illumination light and an imaging optical system for collecting and focusing reflected light from the measurement mark) are inevitable. If there are such aberrations, especially aberrations which are not rotationally symmetric about the optical axis, in the measurement field of view, detection of a measurement mark position will contain errors, so that the obtained overlay measurement value contains a measurement error as a TIS (Tool Induced Shift).
In view of the above, it has been proposed to adjust the position of an illumination aperture stop, an imaging aperture stop or an objective lens included in the measurement optical system of a overlay measuring apparatus before measuring an overlay error using that measuring apparatus (for example in Japanese Patent Application Laid-Open No. 2000-77295).
However, in the prior art as described above, the image position of the illumination aperture stop at the virtual pupil position of the objective lens in the illumination optical system varies depending on the wavelength of the illumination light due to manufacturing errors generated upon mounting the optical parts of the measuring apparatus. The inclination of the principal ray of the illumination light flux (which inclination will be referred to as “illumination telecentricity” hereinafter) varies depending on the color (i.e. the wavelength) and sometimes causes the measurement error TIS depending on the spectral characteristics of measurement marks. In addition, in the imaging optical system also, the image position of the virtual pupil at the position of the imaging aperture stop in the imaging optical system varies depending on the wavelength of the illumination light due of manufacturing errors generated upon mounting the optical parts. This means that diffracted light from the measurement mark is sometimes eclipsed asymmetrically depending on the wavelength range of the reflected light. This can cause the measurement error TIS depending on the spectral characteristics of measurement marks.